GB864645A - Improvements in or relating to rotors of centrifugal fans, compressors, superchargers, pumps and the like, provided with a rotary diffuser - Google Patents

Abstract

864,645. Centrifugal fans, compressors, superchargers and pumps. Dec. 11, 1957 [Oct. 8, 1957], No. 38550/57. Class 110 (1). A bladed rotor for a centrifugal fan, compressor, supercharger pump or the like comprises a rotor having a rotary diffuser formed by an extension of the rotor to beyond the outer edges of the main blades of the rotor, auxiliary blades being provided at the periphery of the rotary diffuser. The front and back plates 8, 9 of a centrifugal impeller are extended at 6, 7 beyond the outer diameter of the impeller blades 10 to form a rotary diffuser. Aerofoil vanes 12, with straight or arcuate camber lines, and backwardly-directed relative to the direction of rotation of the impeller, are provided at the outer periphery of the diffuser, the angle of incidence being either positive or negative as required to produce the desired modification of the pressure-volume characteristic of the impeller. The product of the number of vanes 12 and their chordal length is also selected to produce the desired modification of the characteristic, the ratio of the product to the circumference of the diffuser preferably not exceeding 0.4. Preferably, to avoid slipstream interference, the number of the vanes 12 and that of the impeller blades 10 are prime numbers differing from each other. The blades 10 may be radial, as shown, or may be backwardly inclined at, say, 60 degrees to the circumferential direction. The vanes 12 are bowed as shown in Fig. 9 so that centrifugal force tends to straighten them and therefore to push the plates 6 and 7 further apart at their periphery. Since the centrifugal force on the plates 6 and 7 has the opposite effect of tending to pull the plates 6 and 7 together into less divergent positions, a condition of equilibrium is reached. The vanes 12 may be welded to the plates 6 and 7 or may be made of light alloy or plastics and inserted, as shown in Fig. 9, into slots 18. The slots 18 are closed by welded-on plates 19. The vanes 12 may be hollow and may be thicker at the centre than at the ends so as to form a less deformable beam, and may be bent at the ends to permit fixing by riveting. They may be of flat lamellar form.